Hitherto three types of cold benders have been employed to bend elongated material. The first type is equipped with a forming roll, a mandrel and other dies and bends a pipe by winding it around the forming roll. The second type is equipped with forming dies and can bend a pipe through pressing the dies. The third type is equipped with three rolls and can bend a pipe by feeding the pipe through these rolls which exert pressure while rolling due to an offset arrangement of the rolls.
The first type of bender requires many different forming rolls to provide various curvatures and many mandrels and other dies for different sizes of finished product. This first type of bender is not suitable for large relative radius bending. For the purposes of this disclosure the term "relative radius" means bending radius divided by the diameter of pipe to be bent, R/D. The second and the third types of benders are suitable for large relative radius bending but it is difficult to achieve accurate bending with these devices. The second and third types are not suitable for small relative radius bending.
A device disclosed in Japanese Pat. No. 419,799 may correct some of these defects. That device consists principally of means performing the following functions: supporting and guiding an elongated material to be bent with two pairs of guide rollers at the intermediate part of it, clamping said elongated material at its top end with a clamp connected on a bending arm which can rotate freely around the center of bending, driving said elongated material along its axis at a constant speed, heating said elongated material at the vicinity of said guide roll in a limited narrow circular zone with high frequency induction heating. In this way the elongated material may be bent without the use of forming rolls. The device of Japanese Pat. No. 419,799 solves many problems inherent in the aforementioned three types of benders. However, it is not suitable for very large bending radii for example 50 meters, because the bending radius is limited by the length of bending arm. The device also requires reclamping of the elongated material at a different place to proceed with step of bending, and requires a shifting of the center of bending and a change in the effective length of bending arm in order to change the radius of the bend formed by the device. Likewise, the first type of bender is not able to perform plural bending continuously or not continuously in one process without reclamping.
Accordingly, a primary object of the present invention is to provide an apparatus capable of performing a continuous or discontinuous plural bending of an elongated material including various or variable curvatures as well as normal single bending with a constant curvature.
Another object of the present invention is to provide a method and apparatus for performing not only a single bending of constant radius but a plural bending including various and/or variable bending radius and/or various bending angles in one process, continuously or discontinuously without any reclamping of said elongated material to be bent.
A further object of the present invention is to provide a means for bending continuously or discontinuously, piping components with several bends, for instance, plurally bent pipe used for chemical plants, refineries and many other uses; or expansion bends such as the double offset bend or zigzag bend, and turn piece often used for underground piping.
Yet, a further object of the present invention is to provide a bending apparatus and method which promotes productivity of plural or complex bends and reduces the cost of fabrication of piping making possible new types of compact bends, heretofore impractical to produce because of the need of reclamping the pipe in a convention bender to produce such bends.
These and other objects and features of the invention will become apparent from the claims and from the following description when read in conjunction with the appended drawings.